This project seeks to establish the minimum levels of dietary coumestrol which significantly effects reproduction in animals. Related goals are to describe the mechanism by which impaired reproduction occurs and to assess the probable risk of coumestrol in foods of humans. Coumestrol intakes of greater than 300 ppb (parts per billion) decrease ovulation rates in mice and increase the incidence of abnormal embryos. Current experiments will further define reproductive effects of dietary coumestrol in animals and describe the underlying mechanism of action. Progesterone levels in blood of rats fed known amounts of coumestrol will be measured. Likewise, sodium and potassium balance and tissue content will be determined for potential effects on reproductions. The potential for deposition of coumestrol in body tissues will be determined. Coumestrol will be assayed with time in in vitro rumen digestion systems. Likewise, tissues of animals fed known amounts of coumestrol will be analyzed for residual coumestrol. These data will expand our basic knowledge of phyto-estrogen involvement in mammalian reproduction and the applied question of potential risk to human health.